This invention relates generally to capacitors, and more particularly to capacitors made with oxide dielectrics having high dielectric constants but with reduced leakage current, and to methods of making such capacitors and their incorporation into DRAM cells.
The increase in memory cell density in DRAMs presents semiconductor chip designers and manufacturers with the challenge of maintaining sufficient storage capacity while decreasing cell area. One way of increasing cell capacitance is through cell structure techniques, including three dimensional cell capacitors. The continuing drive to decrease size has also led to consideration of materials with higher dielectric constants for use in capacitors. Dielectric constant is a value characteristic of a material and is proportional to the amount of charge that can be stored in a material when the material is interposed between two electrodes. Promising dielectric materials include BaxSr(1−x)TiO3 (“BST”), BaTiO3, SrTiO3, PbTiO3, Pb(Zr,Ti)O3 (“PZT”), (Pb,La)(Zr,Ti)O3 (“PLZT”), (Pb,La)TiO3 (“PLT”), KNO3, Nb2O5, Ta2O5, and LiNbO3, all of which have high dielectric constants making them particularly desirable for use in capacitors. However, the use of these materials has been hampered by their incompatability with current processing techniques and their leakage current characteristics.
Attempts have been made to overcome the problems associated with the use of Ta2O5. For example, U.S. Pat. No. 5,768,248 to Schuegraf involves the deposition of a dielectric nitride layer after the removal of an oxide layer on the capacitor plate. A Ta2O5 dielectric layer is then deposited, followed by a second nitride layer. The nitride layer restricts oxidation of the inner capacitor plate during the annealing of the Ta2O5 layer. In U.S. Pat. No. 5,814,852 to Sandhu et al., a primarily amorphous diffusion barrier layer is deposited on the Ta2O5 dielectric layer.
While these techniques have been successful, there remains a need for improved processes for incorporating high dielectric constant oxide dielectrics in capacitor constructions and for capacitors containing these materials.